Reset the codes by disconnecting the battery for 5-10 minutes. This will clear everything out of the PCM.
To check the codes, you either need an OBD2 code reader or a trip down to your local Advanced Auto, Autozone, Napa, etc. Most auto stores now do free code scans, many will give you a print out of the codes and some will even clear them for you.
I have an AutoTap Scanner
that works with my laptop for reading codes and examining sensor data on all OBD2 vehicles with the enhanced data pack for GM vehicles. I use their code definitions whenever I need help with a code that doesn't already have a description in their software. You can simply search through their database to get the description. You may have to know some of the digits from your VIN to get the exact code due to manufacturer and model specific code definitions.
Here's the link to their database:
AutoTap OBD2 Code Database